Enormous financial, medical and scientific efforts have been applied during the past fifty years to address the health problems presented by cancer, a leader killing disease on a global scale. Partial successes have been recorded for treatments employing radiation, surgical procedures, and chemotherapy. However, many difficulties remain. Side effects of both radiation and chemotherapy treatments are frequently severe, and can threaten or terminate a patient's life. Destruction of bone marrow with consequent reduction of blood cell populations lowers the patient's resistance to bacterial and viral infection, and exposes the patient to high risk of opportunistic infection. Chemotherapeutic agents are generally highly toxic substances. Early trials of cytokines, while offering promise, have also shown unexpected side effects. Adjunct therapies, with cell stimulating factors compensating for diminished cell production from reduced bone marrow, and combination therapies (e.g., Interleukin-2 and interferons) are being investigated.
A major improvement in cancer therapy would be provided by an agent which is innocuous or largely nontoxic of itself, but which is capable of generating a lethal entity when appropriately activated or triggered. Activation should be specific and occur only after the agent has concentrated in or bound to the target cancer cell. The sites of cancerous tissues can be generally located prior to therapy using standard techniques with radiolabeled antibodies and/or nuclear imaging scanning procedures.